-LRB- CNN -RRB- -- San Francisco 's public transit strike was in its third day Wednesday , with the financial toll so far likely to top $ 200 million , economists estimate .

Negotiations between Bay Area Rapid Transit and union leaders stretched until nearly 3 a.m. Wednesday , CNN affiliate KGO reported . Progress was made , but no deal was reached .

`` We decided we would make more progress if we get more sleep , '' said Josie Mooney , chief negotiator for the Service Employees International Union in the talks , according to KGO .

The two sides returned to the table at 1 p.m. Wednesday , and California Gov. Jerry Brown appointed two new high-level mediators to handle negotiations , the station reported .

About 400,000 daily commuters use BART .

The Bay Area Council Economic Institute says its `` conservative estimate '' finds that lost worker productivity alone is costing the region at least $ 73 million a day . The loss of economic activity could add tens of millions of dollars to that figure , the council said .

The strike is also having `` a costly environmental impact , '' the council said .

`` Increased traffic congestion is generating almost 16 million pounds of carbon , and wasting almost 800,000 gallons of gas every day at a cost of almost $ 3.3 million . ''

BART planned limited charter bus service for those working on Independence Day in case no deal is reached Wednesday . Regardless of when the strike ends , BART said , it will still take about 18 hours for train service to resume .

The dispute centers on pay and benefits .

Unions asked for a 21 % pay increase . BART initially offered to increase salaries by 4 % over four years , but later proposed an 8 % increase ; that was on top of a 1 % increase scheduled to go into effect Monday .

Roxanne Sanchez , president of SEIU Local 1021 , said workers are fed up .

`` Years of layoffs have affected public safety and services . Crippling cuts have not just made our jobs more difficult , but put undue strain on our livelihoods , our families and our communities , '' she said in a written statement .

`` We are sorry that the actions of ATU and SEIU have caused such a tremendous disruption to the people of the Bay Area , '' BART said in a statement Tuesday announcing `` no indication '' that employees would return to work Wednesday .

`` We are working hard to bring a fair and responsible resolution to labor talks .

BART is the nation 's fifth-largest all-rail train system in the United States , with 44 stations in 26 cities that make up the Bay Area , according to the transit authority .

It handles more than 40 % of Bay Area commuters , according to CNN affiliate KPIX .

A study last year found San Francisco among the 10 cities with the worst commutes .

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NEW : Even if a deal is reached , BART says it will still take 18 hours to resume service

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Gov. Jerry Brown appoints new mediators , CNN affiliate KGO reports

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Increased traffic is generating 16 million pounds of carbon , the Bay Area Council says

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BART normally carries 400,000 daily commuters